To regulate nitrogen oxide exhaust of a diesel car in a real road, real world driving emission (RDE) and world-harmonized light duty test procedure (WLTP) as reinforced exhaust regulations are in effect after July, 2017.
Particularly, to respond RDE reinforced exhaust regulation for nitrogen oxide exhaust suppress during driving of the diesel car in the real road, conventional LNT (Lean NOx Trap) and SCR (Selective Catalytic Reduction) which are post treatment devices of nitrogen desorption are difficult.
Nitrogen oxide purification efficiency of the LNT decreases abruptly in a high temperature and high load, and urea injection of the SCR is difficult in a low temperature and low load to decrease the nitrogen oxide purification efficiency abruptly.
Particularly, the SCR system may not inject urea in a low temperature (ammonia (NH3) generation reaction by hydrolysis of urea solution in a below 170 degrees), and blocking phenomenon in an exhaust pipe occurs during injection in a low temperature condition by urea crystallization reaction to deteriorate nitrogen oxide purification efficiency in a low temperature.
To solve this problem, heat loss needs to be minimized in an exhaust system connected to SCR system.
To decrease heat loss of post treatment converter for purifying gas exhausted from an engine of a conventional technic, insulation material of silica non-woven or ceramic blanket type is attached to metal thin plate or cover having a certain shape and fixed to the converter by welding to prevent inside heat of the converter from emitting outside.
However, in the conventional converter structure, to prevent exhaust gas heat inside the converter transferred to the converter surface from emitting to atmosphere, the insulation material attached to the converter surface insulates the converter, and a metal insulation cover is welded on the insulation material to fix the insulation material to transfer heat through the welded portion to emit heat to insulation material cover around the insulation material. Also, the metal cover is made by molding metal plate. So, it is constrained to make the metal cover to insulate whole parts of the converter.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.